Leak detection for canister purge valve

Abstract

Methods and systems for detecting a leak in a canister purge valve are disclosed. In one example approach, a method comprises indicating a leak in response to a temperature change in a fuel vapor canister coupled to a fuel tank in an emission control system while the engine is in operation and a purge valve is closed.

The invention claimed is: 
     
       1. A method for a vehicle with an engine comprising:
 indicating a leak in response to a temperature change in a fuel vapor canister coupled to a fuel tank in an emission control system while the engine is in operation and a purge valve is closed; 
 wherein indicating the leak in response to the fuel vapor canister temperature change is performed in response to a fault in a pressure sensor coupled to the fuel tank. 
 
     
     
       2. The method of  claim 1 , wherein the temperature change comprises a temperature decrease in the canister. 
     
     
       3. The method of  claim 1 , wherein the temperature change comprises a temperature decreasing below a threshold temperature. 
     
     
       4. The method of  claim 1 , wherein the temperature change comprises a rate of temperature decrease in the canister greater than a threshold. 
     
     
       5. The method of  claim 1 , wherein indicating the leak is further responsive to a pressure sensor coupled to the fuel tank. 
     
     
       6. The method of  claim 5 , wherein indicating the leak responsive to the pressure sensor coupled to the fuel tank comprises indicating a leak in response to a pressure decrease in the fuel tank while the engine is in operation and a purge valve is closed. 
     
     
       7. The method of  claim 1 , wherein the purge valve is disposed in a conduit coupling the canister to an intake of the engine. 
     
     
       8. The method of  claim 1 , wherein the temperature change is compensated for one or more of an ambient temperature, a fuel type, and an altitude. 
     
     
       9. The method of  claim 1 , wherein the fuel vapor canister contains activated charcoal. 
     
     
       10. A method for a vehicle with an engine comprising:
 during engine-on conditions:
 closing or maintaining a purge valve closed; and 
 indicating a leak in response to a temperature change in a fuel vapor canister coupled to a fuel tank in an emission control system; 
 
 wherein indicating the leak in response to the temperature change in the fuel vapor canister comprises indicating a leak in the purge valve. 
 
     
     
       11. The method of  claim 10 , wherein the temperature change comprises a temperature decreasing below a threshold temperature. 
     
     
       12. The method of  claim 10 , wherein the temperature change comprises a rate of temperature decrease in the canister greater than a threshold. 
     
     
       13. The method of  claim 10 , wherein indicating the leak in response to the temperature change in the fuel vapor canister is performed in response to a fault in a pressure sensor coupled to the fuel tank. 
     
     
       14. The method of  claim 10 , wherein indicating the leak is further responsive to a pressure decrease in the fuel tank while the engine is in operation and the purge valve is closed. 
     
     
       15. The method of  claim 10 , wherein during the engine-on conditions, the fuel tank is completely sealed off from atmosphere. 
     
     
       16. A method for a vehicle with an engine comprising:
 indicating a leak in response to a temperature decrease in a fuel vapor canister coupled to a fuel tank in an emission control system while the engine is in operation and a purge valve is closed, where the purge valve is disposed in a conduit coupling the canister to an intake of the engine; and 
 wherein indicating the leak in response to the temperature decrease in the fuel vapor canister is performed in response to a fault in a pressure sensor coupled to the fuel tank. 
 
     
     
       17. The method of  claim 16 , wherein the temperature decrease comprises a temperature decrease below a threshold temperature.